The ROADM is a key component for today's dense-wavelength-division-multiplexing (DWDM) optical communication networks. It provides the ability selectively to drop a channel (i.e., wavelength) from within a band of communication channels as well as provide the introduction of a new information-carrying channel at the same wavelength without interrupting the adjoining channels.
A number of ROADM architectures have been developed, including on-chip planar technology, which is restricted to the use of 1-D interconnections such as fibers, or 2-D interconnections such as an on-chip array of integrated-optic (IO) waveguides and switches. For example, some of these architectures include all-fiber mechanically tuned fiber Bragg grating devices (see, e.g., Nykolak, et al., “All-Fiber Active Add-Drop Wavelength Router,” IEEE Photon. Technol. Lett., vol. 9, no. 5, pp. 605-606, May 1997) and an IO grating switch with IO directional-coupler devices (see, e.g., Shibata, et al., “Semiconductor Monolithic Wavelength Selective Router Using a Grating Switch Integrated with a Directional Coupler,” J. Lightw. Technol., vol. 14, no. 6, pp. 1027-1032, June 1996), an array waveguide grating (AWG) multiplexer with IO thermo-optic switches (see, e.g., Saida, et al., “Athermal Silica-Based Optical Add/Drop Multiplexer Consisting of Arrayed Waveguide Gratings and Double Gate Thermo-Optical Switches,” Electron. Lett., vol. 36, no. 6, pp. 528-529, Mar. 16, 2000), an AWG multiplexer with manually simulated 2×2 switches (see, e.g., Ishida, et al., “Multichannel Frequency-Selective Switch Employing an Arrayed-Waveguide Grating Multiplexer with Fold-Back Optical Paths,” IEEE Photon. Technol. Lett., vol. 6, no. 10, pp. 1219-1221, October 1994), a phased array demultiplexer used in conjunction with 2×2 Mach-Zehnder interferometer electro-optic switches (see, e.g., Vreeburg, et al., “First InP-Based Reconfigurable Integrated Add-Drop Multiplexer,” IEEE Photon. Technol. Lett., vol. 9, no. 2, pp. 188-190, February 1997), an IO electro-optically controlled synthesized grating-structure-based filter (see, e.g., Nolting, et al., “Electro-Optically Controlled Multiwavelength Switch for WDM Cross Connector Application,” IEEE Photon. Technol. Lett., vol. 7, no. 3, pp. 315-317, March 1995), a reflective tunable resonant grating filter placed on a tiltable microelectro-mechanical-system (MEMS) platform (see, e.g., Niederer, et al., “Resonant Grating Filter for a MEMS Based Add-Drop Device at Oblique Incidence,” in IEEE/LEOS Int. Conf. Optical MEMS, Conf. Dig., Aug. 20-23, 2002, pp. 99-100), a free-space linear array of 1-D twisted nematic liquid-crystal device used with diffraction gratings (see, e.g., Patel, et al., “Liquid Crystal and Grating-Based Multiple-Wavelength Cross-Connect Switch,” IEEE Photon. Technol. Lett., vol. 7, no. 5, pp. 514-516, May 1995), and using dual bulk acousto-optic tunable filters (see, e.g., Riza, “Low Interchannel Crosstalk Wavelength Routing Switch Based on Bulk Acousto-Optic Tunable Filters,” in Proc. IEEE LEOS Conf., Nov. 10-13, 1997, vol. 2, pp. 341-342, and, Riza, et al. , “Ultrahigh 47-Db Optical Drop Rejection Multiwavelength Add-Drop Filter Using Spatial Filtering and Dual Bulk Acoustooptic Tunable Filters,” Opt. Lett., vol. 23, no. 12, pp. 945-947, June 1998). The MEMS-micromirror-based add/drop filtering has been proposed and demonstrated in a linear 1-D array in which each micromirror switches one wavelength (see, e.g., Ford, et al., “Wavelength Selectable Add/Drop with Tilting Micromirrors,” presented at the IEEE Lasers and Electro-Optics Society Annu. Meeting, (LEOS), Piscataway, N.J., 1997, Post deadline Paper PD2.3, and, Ford, et al., “Wavelength Add-Drop Switching Using Tilting Micromirrors,” J. Lightw. Technol., vol. 17, no. 5, pp. 904-911, May 1999).